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326 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 21
Libinia mexicana Rathbun
Plate T, Figs. 4, 5; Plate 37, Fig. 1
Libinia mexicana Rathbun, 1892, p. 242, pi. 31, fig. 3; 1925, p. 328, pi.
244, fig. 1.
Type: Young male, holotype, U.S.N.M. No. 16072, length 13.5
mm, width 7.5 mm.
Type locality: Off Shoal Point, near the mouth of the Colorado
River, Gulf of California, Mexico, 10.5 fathoms, Albatross station 3029.
Localities subsequently reported: None. Known only from the type
locality and unique specimen above.
Atlantic analogue: None. A Gulf of California endemic species having as its cognate on the Pacific coast of Lower California the foregoing
Libinia setosa Lockington.
Diagnosis: Carapace with 6 median and 1 hepatic spine. Rostrum
longer than in Libinia setosa, horizontal, channeled beneath. Only one
tooth on basal antennal article. Manus of adult male compressed, fingers
gaping broadly at base. Tip of male abdomen rounded. Male first pleopod
channeled to tip; keel upstanding.
Description: Since the original description is based upon an immature
(13 mm) male specimen, a complete description of a 65 mm male from
San Felipe, Gulf of California, is given. It will be found possible to
compare the Gulf of California species point by point by referring to
the description of its west coast of Lower California cognate, Libinia
setosa, as given by Rathbun (1925, p. 327).
Carapace narrowly pyriform, its width less than its postfrontal length
by the distance from the anterior gastric spine or tubercle to the base of
the rostrum. Rostrum horizontal, considerably longer than broad, tubular, sides subparallel, tip emarginate, the two shallow teeth fringed with
hair, and forming with the coarse and hairy antenna an effective excur-
rent channel.
Median spines six, two gastric, one genital, two cardiac, and one
intestinal; a single spine on either side of anterior gastric spine. Two
marginal spines, one branchial, the other subhepatic; four dorsal branchial spines, the posterior two forming a slightly curved horizontal line
with the anterior cardiac spine, the anterior two with the genital spine.
A prominent preocular spine. A single hepatic spine; a subbranchial spine
below the epimeral suture. Two stout pterygostomian spines, the anterior
acute, the posterior blunt; a blunt spine at anteroexternal angle of basal
segment, a small spine just behind the outer margin of that segment.

326 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 21
Libinia mexicana Rathbun
Plate T, Figs. 4, 5; Plate 37, Fig. 1
Libinia mexicana Rathbun, 1892, p. 242, pi. 31, fig. 3; 1925, p. 328, pi.
244, fig. 1.
Type: Young male, holotype, U.S.N.M. No. 16072, length 13.5
mm, width 7.5 mm.
Type locality: Off Shoal Point, near the mouth of the Colorado
River, Gulf of California, Mexico, 10.5 fathoms, Albatross station 3029.
Localities subsequently reported: None. Known only from the type
locality and unique specimen above.
Atlantic analogue: None. A Gulf of California endemic species having as its cognate on the Pacific coast of Lower California the foregoing
Libinia setosa Lockington.
Diagnosis: Carapace with 6 median and 1 hepatic spine. Rostrum
longer than in Libinia setosa, horizontal, channeled beneath. Only one
tooth on basal antennal article. Manus of adult male compressed, fingers
gaping broadly at base. Tip of male abdomen rounded. Male first pleopod
channeled to tip; keel upstanding.
Description: Since the original description is based upon an immature
(13 mm) male specimen, a complete description of a 65 mm male from
San Felipe, Gulf of California, is given. It will be found possible to
compare the Gulf of California species point by point by referring to
the description of its west coast of Lower California cognate, Libinia
setosa, as given by Rathbun (1925, p. 327).
Carapace narrowly pyriform, its width less than its postfrontal length
by the distance from the anterior gastric spine or tubercle to the base of
the rostrum. Rostrum horizontal, considerably longer than broad, tubular, sides subparallel, tip emarginate, the two shallow teeth fringed with
hair, and forming with the coarse and hairy antenna an effective excur-
rent channel.
Median spines six, two gastric, one genital, two cardiac, and one
intestinal; a single spine on either side of anterior gastric spine. Two
marginal spines, one branchial, the other subhepatic; four dorsal branchial spines, the posterior two forming a slightly curved horizontal line
with the anterior cardiac spine, the anterior two with the genital spine.
A prominent preocular spine. A single hepatic spine; a subbranchial spine
below the epimeral suture. Two stout pterygostomian spines, the anterior
acute, the posterior blunt; a blunt spine at anteroexternal angle of basal
segment, a small spine just behind the outer margin of that segment.